The shoulder or deltoid muscle is made up of three sets of muscles or muscle fibers, specifically anterior fibers, lateral fibers, and posterior fibers, referring to the location on the shoulder. In order to perform a lateral deltoid exercise, the arms are rotated outward and upward about the shoulder joint. This exercise can be performed as a free weight exercise, with the arms initially hanging at the sides of the body and the hands gripping dumbbells with the palms facing inward and elbows bent.
In known lateral deltoid machines, the user is seated in a stationary position and engages arm pads on exercise arms at each side of the seat with their arms bent at the elbow and their hands gripping handles at the ends of the exercise arms. The arms are then rotated to push the exercise arms upward and outward against an exercise resistance or load. This type of exercise does not exercise all of three sets of shoulder or deltoid muscles evenly.